Transmitter for communications system

ABSTRACT

An rf signal transmitter for transmitting rf signals through a plurality of antennas is described, which comprises: a transmit section adapted to selectively set, with respect to an input signal, the initial phase of an output to at least one of said antennas depending on a time or frequency region used for communication and to provide delay to the output on an antenna-by-antenna basis and on the basis of a transmission timing or a transmission frequency; and a quality information receive section for receiving quality information from destination station, i.e., a wireless terminal unit, said quality information concerning the rf signal transmitted from said transmit section and received at said destination station.

This application is a Divisional of application Ser. No. 12/097,865,filed on Jun. 17, 2008, now U.S. Pat. No. 8,224,263, for which priorityis claimed under 35 U.S.C. §120. U.S. patent application Ser. No.12/097,865 is the national phase of PCT International Application No.PCT/JP2006/325282 filed on Dec. 19, 2006 under 35 U.S.C. §371, whichclaims priority on Japanese Patent Application No. 2005-366590 filedDec. 20, 2005, the contents of which are incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to a radio frequency (rf) signaltransmitter and, particularly to a transmitter for transmitting rfsignals through a plurality of antennas.

BACKGROUND ART

In recent years, it has been proposed in multiple carriertransmission-related technology to divide, for user scheduling, thetime-frequency plane into a plurality of blocks of regions arrangedalong the frequency and time axes. It is noted in this connection thatthe region defined by the frequency and time axes and secured for anindividual user's communication is referred to as an assigned slot, andthat a basic block of such regions for designating the assigned slots isreferred to as a chunk.

In the transmission of broadcast/multicast signals and/or controlsignals, blocks distributed in a broad frequency region are assigned toachieve frequency diversity effect and

Conversely, in the transmission of unicast signals for one rftransmitter-to-one rf receiver communication, it has been proposed thatblocks distributed in a narrower frequency region be assigned to achievea multiuser diversity effect (Non-Patent Documents 1, 2 and 3 referredto).

-   [Non-Patent Document 1]: “Downlink Multiple Access Scheme for    Evolved UTRA,” Apr. 4, 2005, R1-050249, 3GPP (URL:    ftp://ftp.3gpp.org/TDG_RAN/WG1_RL1/TSGR1_(—)40bis/Docs/R1-050249.zip)-   [Non-Patent Document 2]: “Physical Channel and Multiplexing in    Evolved UTRA Downlink,” Jun. 20, 2005, R1-050590, 3GPP (URL:    ftp://ftp.3gpp.org/TSG_RAN/WG1_RL1/R1_Ad_Hocs/LTE_AH_JUNE-05/Docs/R1-050590.zip)-   [Non-Patent Document 3]: “Intra-Node B Macro Diversity Using    Simultaneous Transmission with Soft-combining in Evolved UTRA    Downlink,” Aug. 29, 2005, R1-050700, 3GPP (URL:    ftp://ftp.3gpp.org/tsg_ran/WG1_RL1/TSGR1_(—)42/Docs/R1-050700.zip)

FIGS. 33 and 34 show the distribution in time (vertical axis)-frequency(horizontal axis) plane of signals to be transmitted from an rftransmitter to an rf receiver. Referring to FIG. 33, time and frequencyare shown along the vertical and horizontal axes, respectively. Uniformtransmission time width t1 to t5 are defined along the vertical axis.Also, transmission frequency bands f1 to f4 are defined along thehorizontal axis, with a uniform bandwidth Fc. As shown in FIG. 33, timewidths t1 to t5 and frequency bands f1 to f4 define twenty (20) chunksK1 to K20.

Referring to FIG. 34, four chunks K1 to K4 arranged along the frequencyaxis are combined into one frequency-broadened chunk of frequencybandwidth 4 f 1, which is then divided into three slots S1 to S3 of auniform length of t1/3. Slots S1 to S3 are then assigned to a first to athird users, respectively, with the users enjoying the benefit offrequency diversity.

Then, chunk K5 is used as assigned slot S4 for a fourth user. Similarly,chunks K6 and K7 are combined to form an assigned slot S5 for a fifthuser, while chunk K8 is used as an assigned slot S6 for a sixth user.Thus, the fourth to the sixth users enjoy the benefit of the multiuserdiversity effect.

Similarly, chunks K9 and K11 are used as assigned slot S7 for a seventhuser.

On the other hand, chunks K10 and K12 are divided along the time axisinto three portions of equal length t3/3 of a frequency bandwidth of 2 f2 to form slots S8 to S10, which are assigned to an eighth to a tenthusers, respectively. Thus, the seventh to tenth users enjoy the benefitof frequency diversity effect.

Similarly, chunks K13 and K14 are used as assigned slots S11 and S12 foran eleventh and a twelfth users, respectively. On the other hand, chunksK15 and K16 are combined into a broader-band assigned slot S13 for athirteenth user. Thus, the eleventh to thirteenth users enjoy thebenefit of multiuser diversity effect.

Moreover, chunks K17 and K19 are combined into an assigned slot S14 fora fourteenth user. On the other hand, chunks K18 and K20 are combinedinto slots S15 to S17 of a frequency bandwidth of 2 f 2 and a timelength of t5/3. Slots S15 to S17 are assigned to a fifteenth to aseventeenth users, respectively. Thus, the fourteenth to seventeenthusers are benefited by a frequency diversity effect.

The problem associated with the conventional technology described aboveis that the multiuser diversity effect is not adequately achieveddepending on the location of the mobile terminal unit user and theassociated slot assigned thereto.

DISCLOSURE OF INVENTION

According to the present invention, there is provided an rf signaltransmitter for transmitting such signals through a plurality ofantennas, comprising: a transmit section adapted to selectively set,with respect to an input signal, the initial phase of an output to atleast one of said antennas depending on time or frequency region usedfor communication and to provide delay to the output on anantenna-by-antenna basis and on the basis of transmission timing ortransmission frequency; and a quality information receive section forreceiving such quality information from a destination station concerningthe rf signal transmitted from said transmit section.

According to one aspect of the invention, there is provided an rf signaltransmitter of the type described above, wherein said transmit sectionprovides said initial phase and said delay to each of the chunks formedby dividing each of the rf signal frames of a predetermined length oftime extending over the entire frequency band assigned forcommunication.

According to another aspect of the invention, there is provided an rfsignal transmitter further comprising a scheduling section adapted toassign each of said terminal units to a specific chunk, based on thescheduling of said initial phase and said delay provided by saidtransmit section.

According to still another aspect of the invention, there is provided anrf signal transmitter, wherein said transmit section is adapted tochange the amount of said delay, to thereby give an optimum diversityeffect to each of said chunks.

According to still another aspect of the invention, there is provided anrf signal transmitter, wherein the selective setting of said delay atsaid transmit section is performed by selecting one out of a pluralityof delay amounts provided in advance in said transmit section.

According to still another aspect of the invention, there is provided anrf signal transmitter, wherein said diversity effect is either afrequency diversity effect or a multiuser diversity effect, and whereinthe amount of said delay given to said chunk for achieving the frequencydiversity effect is greater than that given to said chunk for achievingthe multiuser diversity effect.

According to still another aspect of the invention, there is provided anrf signal transmitter, wherein said chunk belongs to a region whereeither the frequency diversity effect or the multiuser diversity effectis achieved, and wherein said transmit section is adapted to set saidinitial phase at a value common to all the chunks belonging to theregion where the frequency diversity effect is achieved.

According to still another aspect of the invention, there is provided anrf signal transmitter, wherein said chunk includes a pilot signal forassessing receive signal quality and a common data signal fortransmitting data, and wherein the amount of said initial phase and saiddelay in one of said chunks is the same for both said pilot signal andsaid common data signal contained in said chunk.

According to still another aspect of the invention, there is provided anrf signal transmitter, wherein said scheduling section includes: meansfor deciding on the priority of a plurality of said terminal unitsthrough comparison of information concerning said receive signal qualityreceived from each of said terminal units; and means for assigning aspecific chunk to each of said terminal units on the basis of saidpriority.

According to still another aspect of the invention, there is provided anrf signal transmitter, wherein the initial phase of a chunk beingprocessed at said priority deciding means is equal to that of a chunkbeing processed at said assigning means.

According to still another aspect of the invention, there is provided anrf signal transmitter, wherein the amount of delay set for said chunkbeing processed at said priority deciding means is equal to that of achunk being processed at said assigning means.

According to still another aspect of the invention, there is provided anrf signal transmitter, wherein said scheduling section performs, on aframe-by-frame basis, the operation of assigning said terminal unit to aspecific chunk in a frame, and wherein the amount of said initial phaseor said delay set by said transmit section for a chunk lying at the sameposition in said frame is common to all said frames.

According to still another aspect of the invention, there is provided anrf signal transmitter, wherein said transmit section sets the amount ofsaid initial phase or said delay at the same value at a predeterminedrepetition period.

According to still another aspect of the invention, there is provided anrf signal transmitter, wherein said scheduling section is adapted toassign to a terminal unit a communication time region defined by thelapse of the prefixed round trip time after receipt from the terminalunit of information concerning the quality of the receive signal, andwherein said repetition period is said round trip time multiplied by thereciprocal of a natural number.

According to still another aspect of the invention, there is provided anrf signal transmitter, wherein said transmit section is adapted to giveas said delay a phase rotation of 2πfm·nT (T stands for a prefixed time)to said signal to be transmitted through the n-th one of said antennasby a subcarrier of a frequency differing from the 0-th subcarrier by fm.

According to still another aspect of the invention, there is provided anrf signal transmitter, wherein said transmit section decides the amountof said initial phase to be given to each of said chunks, on the basisof said information concerning receive signal quality.

According to still another aspect of the invention, there is provided anrf signal transmitter, wherein the number of chunks to which the sameamount of the initial phase is given, is decided on the basis of saidinformation concerning receive signal quality.

According to still another aspect of the invention, there is provided anrf signal transmitter, wherein the selective setting of said initialphase at said transmit section is performed by selecting one out of aplurality of initial phase values provided in advance in said transmitsection.

According to still another aspect of the invention, there is provided anrf signal transmitter, wherein said transmit section is adapted to giveas said initial phase a phase rotation of Φn to a signal to betransmitted through the n-th one of said antennas, and wherein thedifference, in the same timing and in the same frequency, between saidΦn and another phase rotation Φ0 given to the 0th antenna as initialphase is equal to one out of K mutually different values (K: naturalnumber), where the K different values are given by 2πk/K (k=0, 1, 2, . .. , K−1).

The rf signal transmitter of the present invention, wherein the transmitsection is adapted to give the input signal the initial phase, whichselectively sets the amount of delay given to the output to at least oneof the antennas, has the advantage of permitting the multiuser diversityeffect to be achieved even in time domain, resulting in excellentmultiuser diversity effect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows in blocks an rf communication system, which employs an rfsignal transmitter 1 according to a first embodiment of the presentinvention.

FIG. 2A schematically shows signal delay profile used in the aboveembodiment.

FIG. 2B schematically shows a transfer function associated with theabove embodiment.

FIG. 3A schematically shows signal delay profile used in the aboveembodiment.

FIG. 3B schematically shows another transfer function associated withthe above embodiment.

FIG. 3C shows still another transfer function associated with the aboveembodiment.

FIG. 4A schematically shows the maximum signal delay associated with theembodiment.

FIG. 4B shows the relationship of the maximum delay amounts shown inFIG. 4A to frequency change.

FIG. 5A shows maximum delay amounts associated with the embodiment.

FIG. 5B shows the relationship of the maximum delay amounts shown inFIG. 5A to frequency change.

FIG. 6A illustrates the transmission in the above embodiment of a commonrf signal through a plurality of antennas without any delay applied tothe signal.

FIG. 6B shows the frequency distribution of receive signal power at rfreceiver 9 shown in FIG. 6A.

FIG. 6C shows the frequency distribution of receive signal power at anrf receiver 10.

FIG. 7A illustrates the transmission in the above embodiment of a commonrf signal from a plurality of antennas with mutually different delayamounts introduced at respective antennas.

FIG. 7B shows the frequency distribution of receive signal power at anrf receiver 9 shown in FIG. 7A.

FIG. 7C shows the frequency distribution of receive signal power at anrf receiver 10 shown in FIG. 7A.

FIG. 8 shows how the chunk in the embodiment is structured.

FIG. 9 illustrates the state where a plurality of (three in number)wireless mobile terminal units are in communication with a base station.

FIG. 10 shows transfer functions C11 and C12 of terminal unit 12 in theabove embodiment for multiuser diversity region and frequency diversityregion, respectively, in conjunction with the makeup of the chunk.

FIG. 11 shows transfer functions C21 and C22 of terminal unit 14 in theabove embodiment for multiuser diversity region and frequency diversityregion, respectively, in conjunction with the makeup of the chunk.

FIG. 12 shows a transfer function for chunks K1 to K4 associated withterminal unit 12 in the embodiment.

FIG. 13 shows transfer functions and the chunk makeup for the case wherethe initial phase of an rf signal transmitted from one antenna isselectively set on a slot-by-slot basis.

FIG. 14 shows the variation in receive signal level for the case wherethe initial phase is selectively set in the above embodiment dependingon the multiuser diversity region and frequency diversity region.

FIG. 15 shows an example of reported transmission rate values (CQI) foreach of the chunks at terminal unit 12 in the embodiment.

FIG. 16 shows an example of reported transmission rate values (CQI) foreach of the chunks at terminal unit 13 in the embodiment.

FIG. 17 shows an example of reported transmission rate values (CQI) foreach of the chunks at terminal unit 14 in the embodiment.

FIG. 18A shows an example of the prioritization of terminal units 12 to14 in the embodiment with respect to phase p1.

FIG. 18B shows an example of the prioritization of terminal units 12 to14 in the embodiment with respect to phase p2.

FIG. 19 shows an example of scheduling based on the prioritization shownin FIGS. 18A and 18B.

FIG. 20 shows another example of scheduling based on the prioritizationshown in FIGS. 18A and 18B.

FIG. 21 shows the makeup of the chunk for the case where the proportionof the number of chunks to which the respective initial phases areapplied is adaptively controlled.

FIG. 22 shows how the initial phase is selectively set in the secondembodiment of the present invention.

FIG. 23 shows the relationship between the receive signal levelvariation and the scheduling round trip time RTT for the secondembodiment.

FIG. 24 shows an example of the receive signal level variation atterminal units 12 and 13 in the embodiment.

FIG. 25 shows an example of scheduling for the case where a mutuallydifferent initial phase is set for each of the chunks in the embodiment.

FIG. 26 shows an example of the phase difference of two signals and thecomplex amplitudes of the two signals as combined.

FIG. 27 shows frequency characteristics and the chunk makeup for thecase where four different initial phases are used in the thirdembodiment of the invention.

FIG. 28 shows in blocks the makeup of a base station unit according tothe fourth embodiment of the invention.

FIG. 29 shows a flowchart for describing the operation of a schedulerunit 19 in the fourth embodiment.

FIG. 30 shows an example of MSC information in the embodiment.

FIG. 31 shows in blocks the makeup of a transmit section 21 employed inthe embodiment.

FIG. 32 shows in blocks the makeup of a transmit section 21 employed inthe fifth embodiment.

FIG. 33 shows an example of the time-frequency relationship for an rfsignal transmitted from an rf transmitter to an rf receiver according toa conventional technique.

FIG. 34 shows another example of the time-frequency relationship for anrf signal transmitted from an rf transmitter to an rf receiver accordingto a conventional technique.

REFERENCE SYMBOLS

-   -   1 denotes rf signal transmitter;    -   2, 3 and 4, transmission antennas;    -   5 and 6, delay means;    -   7, rf signal receiver;    -   8, rf signal transmitter;    -   9 and 10, rf signal receiver;    -   11, base station;    -   12, 13 and 14, wireless terminal units;    -   15, packet data convergence protocol (PDCP) unit;    -   16, radio link control (RLC) unit;    -   17, media access control (MAC) unit;    -   18, physical layer;    -   19, scheduler;    -   20, transmit unit controller;    -   21, transmit unit;    -   22, receive unit;    -   23, radio frequency conversion unit;    -   24, 25 and 26, antennas;    -   110 x and 110 y, user-by-user signal processors;    -   111, error correction coding unit;    -   112, modulation unit;    -   120, pilot signal generator;    -   130, subcarrier assignment unit;    -   140 a, 140 b and 140 c, antenna-by-antenna signal processors;    -   141, phase rotation unit;    -   142, inverse fast Fourier transform (IFFT) unit;    -   143, parallel-to-serial converter;    -   144, guard interval insertion unit;    -   145, filter;    -   146, D-A converter;    -   210 x and 210 y, user-by-user signal processors;    -   211, error correction coding unit;    -   212, modulation unit;    -   213, subcarrier assignment unit;    -   214, IFFT unit;    -   215, parallel-to-serial converter;    -   216, circulating delay insertion unit;    -   230 a, 230 b and 230 c, antenna-by-antenna signal processors;    -   231, signal combining unit;    -   232, guard interval insertion unit;    -   233, filter; and    -   234, D-A converter.

BEST MODE FOR CARRYING OUT THE INVENTION

A first embodiment of the present invention will now be describedreferring to the drawings. In FIG. 1, which schematically shows thesignal transmitted from a rf signal transmitter 1 to an rf signalreceiver 7 through a plurality of transmission paths, the transmitter 1has antennas 2, 3 and 4, to which the transmit signal is supplieddirectly, through a delay means 5 of a delay T and additionally, througha delay means 6 of a delay T, respectively, so that antennas 2, 3 and 4may transmit the same rf signal with a delay of 0, T and 2T,respectively. The rf signal receiver 7 receives the rf signaltransmitted from the transmitter 1. While the transmitter 1 has threeantennas 2 to 4, these antennas may be those located in the same sector,or in mutually different sectors within the coverage of the same basestation, or in mutually different coverages of base stations, assumingthat the transmitter 1 constitutes a base station unit for a mobiletelephone system. It is assumed in this specification that threeantennas are located in the same sector. It is also assumed as describedabove that each of the delay means 5 and 6 provides a delay time T,thereby to give a delay T to the rf signal transmitted from the antenna3, while giving a delay 2T to the rf signal transmitted from antenna 4.

FIGS. 2A and 2B show, respectively, a signal delay profile and transferfunction for a plurality (3 in number) of the rf signals transmittedthrough mutually different transmission paths, which involve the threedelay times of 0, T and 2T mentioned above. FIG. 2A shows, with respectto the lapse of time (horizontal axis), the magnitude of signal power(vertical axis) of the three rf signal components transmitted to reachthe rf receiver through the three transmission paths involving the threedelay times mentioned above. More specifically, received signal powerhas a maximum delayed component at 2T+dmax, which is significantlylarger than the corresponding component of received signal power whenthe same rf signal is transmitted at the same timing. It should be notedhere that dmax stands for the difference in reception timing between therf signals, which have been transmitted through the longest and shortesttransmission paths, respectively.

Referring to FIG. 2B, which shows a transfer function in terms of thereceive signal power based on the Fourier transform of the delay profilein the time domain as shown in FIG. 2A, the large delayed componentobserved at 2T+dmax in the delay profile means a steep variation in thetransfer function in frequency domain. Therefore, data D1 and D2 arespread with a spreading ratio of 4 as shown in FIG. 2B, to which asubcarrier is assigned. While it is desirable in this connection tocontrol, on the transmitter 1 side, the spreading ratio or the codingrate for the error-correction code depending on the variation in thetransfer function. The spreading ratio or the coding rate for theerror-correction code can be determined independently of thefrequency-dependent variation of the characteristics of the transmissionpath because the delay 2T is known on the transmitter 1 side.

If a multiuser diversity effect is to be achieved, the maximum delay2T+dmax for instantaneous delay profile should not preferably be verylarge. FIGS. 3A to 3C show a delay profile and transfer functions forthe receive signals transmitted through paths involving mutuallydifferent delay times. More particularly, FIG. 3A shows, with respect tothe lapse of time (horizontal axis), the magnitude of signal power(vertical axis) of the three rf signal components transmitted throughthree transmission paths involving mutually different delay time. On theother hand, FIGS. 3B and 3C show transfer functions observed at the rfsignal receivers of users u1 and u2, respectively. Due to the differencein location of the users u1 and u2, the transfer function for any momentobserved at the receiver of one of them differs from that observed atthe receiver of the other. More definitely, assuming that the left-handand right-hand regions of the curves shown in FIGS. 3B and 3C are forfrequency channels b1 and b2, respectively, the receiver of user u1enjoys the benefit of the better transmission quality of frequencychannel b2, while the receiver of user u2 enjoys a better qualityreception at frequency channel b1. Thus, the transmission of data D1-D4to user u1 is performed through frequency channel b2, while thetransmission of data D1-D4 to user b2 is performed through frequencychannel b1.

As described above, multiuser diversity effect, which can enhancetransmission efficiency of a wireless communication system, is achievedby allowing mutually different users to use mutually different frequencychannels, thereby to utilize a frequency channel of better transmissionquality for any given moment. However, when the maximum delay time2T+dmax is set at a value which is excessively large, the transferfunction comes to suffer steeper variation in terms of frequency, withthe result that the difference in transmission quality between frequencychannels b1 and b2 becomes smaller. To achieve adequate multiuserdiversity effect, the maximum delay time 2T+dmax should be set at avalue which is sufficiently small.

FIGS. 4A, 4B, 5A and 5B show the relationship between the maximum delaytime (n−1)T shown in the time domain and the variation in transferfunction shown in the frequency domain. When the transmitted rf signalis received at the receiver with power w31 and w32 with a delay (n−1)T,the transfer function of the transmission path from the transmitter tothe receiver is as shown in FIG. 4B, with the frequency spacing of thesteep drop in the receive power (vertical axis) defined by F=1/(n−1)T.Similarly, when the transmitted rf signal is received, as shown in FIG.5A, at the receiver with a power of w41, w42 and w43, with the lastsignal power w43 received (n−1)T later than the first signal power w41,the frequency spacing of the steep drop in the receive power (verticalaxis) is defined also by F=1/(n−1)T.

As described above, when frequency diversity effect is to be achieved,the transfer function should exhibit variation at a frequency differentfrom that for the case where the multiuser diversity effect is to beachieved. Therefore, when the frequency diversity effect is pursued, anenvironment suited for the achievement of such effect is realized bysetting (n−1)T>Fc, where the maximum delay time (n−1)T is set by thetransmit antenna-to-transmit antenna spacing, and the frequencybandwidth Fc is assumed for the chunk which is the basic region definedby the time-frequency plane for securing the user-to-user communication.In contrast, when the multiuser diversity effect is pursued, anenvironment suited for the achievement of such effect is realized bysetting (n−1)T<1/Fc, where the maximum delay time (n−1)T is set by thetransmit antenna-to-transmit antenna spacing. In the description givenbelow, when (n−1)T<1/Fc is set, it includes (n−1)T=0. While it isassumed in the description below that the delay time introduced by theuse of the plurality of transit antennas is given by T multiplied by(n−1) with T assumed to be constant, the antennas may have mutuallydifferent values for T. Also, when the multiuser diversity effect ispursued, the number of transmit antennas may be reduced, instead ofsetting (n−1)T<1/Fc, thereby to shorten the maximum delay time.

As described above, the frequency diversity effect or the multiuserdiversity effect can be achieved without being affected by theconditions of the transmission paths, by setting (n−1)T>1/Fc or(n−1)T<1/Fc, depending on whether the rf signal is transmitted based onfrequency diversity or multiuser diversity.

The transmission on the basis of frequency diversity or multiuserdiversity can be chosen, depending on the type of signals to betransmitted (e.g., pilot signal, control signal, broadcast/multicastsignal, etc.), or the rate of change in location of the transmitter(frequency diversity for fast-moving transmitter and multiuser diversityfor slow-moving transmitter, etc.).

FIGS. 6A-6C illustrate the operation of the system, wherein an rf signaltransmitter 8 transmits the same rf signal simultaneously from aplurality of antennas without giving any delay therebetween. Assumingthat an rf signal transmitter 8 is used with a plurality (3 in number)of horizontally non-directional antennas arranged in parallel with eachother as shown in FIG. 6A, elliptical lobes e11 and e12 are formed in aradiation pattern as shown in FIG. 6A. As a result, there will be aregion where the rf signals will be received by a receiver 9, forexample, at a relatively high receive signal power level throughout theentire frequency band (see FIG. 6B), while there will be another regionwhere the rf signals are received at a relatively low receive signalpower level throughout the entire frequency band (see FIG. 6C).

FIGS. 7A-7C illustrate the operation of the system, where rf signaltransmitter 8 transmits the same rf signal giving mutually differentdelay time to the respective signals. Assuming that the rf signaltransmitter 8 is used with a plurality (3 in number) of horizontallynon-directional antennas arranged in parallel with each other as shownin FIG. 7A, the average receive signal level at the rf signal receiver 9is kept substantially constant (see FIG. 7B) regardless of thedirection, although there will be the rf receive signal frequencyregions where the receive signal power level is high or low, due to theelliptical lobes e21-e26 of the radiation pattern as shown in FIG. 6A,with the result that the transmission quality at the receive signallevel of the rf receiver 9 (FIG. 7B) and that of an rf receiver 10 (FIG.7C) can be made comparable to each other. Thus, the transmission of rfsignals from the rf transmitter 8 with a mutually different delay timegiven to the signals at transmission antennas can dissolve the defectinvolved in the system shown FIGS. 6A and 6B where the same rf signalsare transmitted simultaneously through a plurality of transmissionantennas without any delay as shown in FIGS. 6A to 6C.

FIG. 8 shows how the signals are arranged in chunk K1 shown in FIG. 1.Referring to FIG. 8, chunk K1 includes nineteen (19) subcarriers S1 toS19 arranged along the horizontal (frequency) axis, and four (4)orthogonal frequency division multiplexed (OFDM) symbols sm arrangedalong the vertical (frequency) axis. Hatched portions P1 to P10 denotecommon pilot channels for transmitting the Common Pilot Channel (CPICH)signals, which are for estimating the condition of the transmissionpaths at the time of demodulation and for determining the quality of thereceived rf signal. Those portions of the chunk other than theabove-mentioned hatched portions are common data channels fortransmitting common data signals. It should be noted here that chunks K1to K20 are of the same signal structure.

Referring now to FIG. 9, mobile terminal units 12, 13 and 14 located inthe area surrounding a base station unit 11, which includes an rf signaltransmitter embodying the present invention, are in communication withthe base station unit 11. The base station unit 11 defines three sectorsSC1-SC3, each of which has a plurality of (e.g., three) antennas. Itwill be recognized here that the three mobile units mentioned above arein communication with sector SC1 in the manner described above inconjunction with FIG. 1.

FIG. 10 shows in its upper portion transfer functions C11 and C12observed in the multiuser diversity region and in the frequencydiversity region, respectively, with the rf signal power and frequencytaken along the vertical and the horizontal axes, respectively. It willbe noted in FIG. 10 that the transfer functions observed at the mobileterminal unit 12 of FIG. 9 are shown as transfer functions C11 and C12.

FIG. 10 also shows in its lower portion the manner similar to FIG. 1, inwhich chunks K1-K20 are assigned to the users for communication. In FIG.10, the chunks are divided into four groups, i.e., a group L11consisting of chunks K1, K5, K9, K13 and K17; a group L12 consisting ofchunks K2, K6, K10, K14 and K18; a group L13 consisting of chunks K3,K7, K11, K15 and K19; and a group L14 consisting of chunks K4, K8, K12,K16 and K20; with the groups L11 and L13 covering the multiuserdiversity region and with the groups L12 and L14 covering the frequencydiversity region.

It follows therefore that when the transfer function of the transmissionpath is calculated for mobile terminal unit 12 using the common pilotsignal CPICH of the chunk included in the group L11, the portion of thetransfer function C11 lying in the frequency band f1 is observed.Similarly, when the transfer function of the transmission path iscalculated using the common pilot signal CPICH of the chunk included inthe group L12, the frequency band f2 portion of the transfer functionC12 is observed and, when the transfer function of the transmission pathis calculated using the common pilot signal CPICH of the chunk includedin the group L13, the frequency band 13 portion of the transfer functionC11 is observed and, when the transfer function of the transmission pathis calculated using the common pilot signal CPICH of the chunk includedin the group L14, the f4 portion of the transfer function C12 isobserved. It is noted here that the division of chunks K1-K20 intogroups L11-L14 for assignment to the multiuser diversity region and thefrequency diversity regions may be kept unchanged from the system designstage or may be dynamically changed depending on how the mobile terminalunits are used (the number of such units, that of high-speed mobileunits and the amount of data being transmitted, etc.).

FIG. 11 shows the transfer function as observed at the mobile unit 14shown in FIG. 9, and the division of the chunks into groups. Morespecifically, the upper portion of FIG. 11 shows transfer functions C21and C22 observed in the multiuser diversity region and the frequencydiversity region, respectively, with the rf signal power and frequencytaken along the vertical and the horizontal axes, respectively. It willbe noted from the comparison of FIGS. 10 and 11 that transfer functionsC21 and C22 differ from transfer functions C11 and C12 due to thedifference in location where the transmission path is observed.

FIG. 11 also shows in its lower portion the manner similar to FIG. 10 inwhich the chunks K1-K20 are assigned to the users for communication. InFIG. 11, the chunks are divided into four groups, i.e., the group L11consisting of the chunks K1, K5, K9, K13 and K17; the group L12consisting of chunks K2, K6, K10, K14 and K18; the group L13 consistingof the chunks K3, K7, K11, K15 and K19; and the group L14 consisting ofthe chunks K4, K8, K12, K16 and K20; with the groups L11 and L13covering the multiuser diversity region and with the groups L12 and L14covering the frequency diversity region.

It follows therefore that when the transfer function of the transmissionpath is calculated, as in the case of FIG. 10, for mobile terminal unit14 using the common pilot signal CPICH of the chunk included in thegroup L11, the frequency band f1 portion of transfer function C21 isobserved. Similarly, the frequency band f2 portion of the transferfunction C22, the frequency band f3 portion of the transfer functionC21, and the frequency band f4 portion of the transfer function C22 areobserved, when the transfer function of the transmission path iscalculated using the common pilot signal CPICH of chunk included in thegroups L12, L13 and L14, respectively.

If information indicative of the quality of a received signal istransmitted from each of the mobile units to the base station as a partof the Channel Quality Indicator (CQI) signal, the comparison isperformed at the base station between groups L11 and L13 for the mobileterminal 12, i.e., between the frequency band f1 portion and thefrequency band f2 portion of the transfer function C11 for the qualityof received signal and, based on the comparison results, the basestation assigns group L11 (or frequency band f1) to mobile terminal 12for transmission of the rf signal.

In the case of mobile terminal 14, the base station performs thereceived signal comparison between the groups L11 and L13, i.e., betweenthe f1 portion of transfer function C21 and the f3 portion of transferfunction C21 and, based on the comparison results, assigns the group L13(or frequency band f3) to the mobile terminal 14 for transmission of therf signal.

It will be understood from the foregoing that even when a mutuallydifferent delay time is inserted at the base station on a transmitantenna-by-transmit antenna basis for the frequency diversity region andthe multiuser diversity region, an appropriate chunk can be assigned toeach of the mobile terminal units to achieve an adequate multiuserdiversity effect by applying the scheduling based on the CQI signalsupplied from each of the mobile terminal units, with the frequencydiversity region and the multiuser diversity region determined inadvance and with the common pilot signal contained therein having theabove-mentioned mutually different delay time introduced on a transmitantenna-by-transmit antenna basis.

Description will now be given on the situation where the initial phaseof the rf signal transmitted from at least one of the antennas ischanged on a slot-by-slot basis or on a basis of a plurality of slots.

FIG. 12 shows transfer function of actual transmission path observed atmobile terminal 12 involving the chunks K1-K4 shown in FIG. 10. It willbe noted in FIG. 12 that the f1 and f3 portions of the transfer functionexhibit steep variation in frequency domain because the chunks K1 andK3, i.e., the groups L11 and L13, have a delay time applied thereto toachieve the multiuser diversity effect. On the other hand, the f2 and f4portions of the transfer function exhibit more moderate variation in thefrequency domain, compared with the f1 and f3 portions, because chunksK2 and K4, i.e., the groups L12 and L14 have a delay time appliedthereto to achieve the frequency diversity effect.

Transfer functions of the transmission paths observed for mobileterminal units other than the terminal unit 12 similarly exhibit moremoderate variation in the f2 and f4 portions than in the f1 and f3portions. It will be noted however that the positions of the peak valuesin the transfer function differ from one terminal unit to another,because the multipath-based phase difference appearing in thetransmitted signal components differs depending on where the terminalunit is located.

FIG. 13 illustrates how the initial phase is selectively set in the timedomain on a slot-by-slot basis for the rf signal transmitted from atleast one of the antennas. While it is assumed in the description belowthat two different initial phase amounts are selected, there may be morethan two different initial phase amounts.

The lower portion of FIG. 13 shows the setting of the initial phase at afirst phase p1 for the chunks K1 to K4 and K9 to K12, and the setting ofthe initial phase at a second phase p2 for the chunks K5 to K8 and K13to K16.

The upper portion of FIG. 13 shows frequency characteristics of thetransfer function for the initial phase of value p1 at terminal unit 12and that for the initial phase of value p2 at the same terminal unit. Itwill be noted that the peak values of the frequency characteristiccurves shift in frequency domain depending on the initial phase set onthe rf signal side, due to the multipath interference.

As described above, while the transmission path conditions are estimatedand the receive signal quality is measured on the basis of common pilotsignals inserted on the transmit side to each of the chunks, the signalquality measurements differ depending on the initial phase selectivelyset on the transmit side, due to the common pilot signal being adverselyaffected by the multipath interference. When the transmission path isexperiencing a low-rate variation, two different initial phase valuesmay be alternately selected on a slot-by-slot basis as shown in FIG. 13,to thereby provide two different frequency characteristics alternatelyon a slot-by-slot basis.

The change in the values of initial phase results in the change inreceive signal power level (receive signal quality) between the regionwhere the delay time suited for achieving a multiuser diversity effectis selected and the region where the delay time suited for achieving thefrequency diversity effect is selected. FIG. 14 shows an example of thereceive signal level variation in the frequency band f1 where the delaytime suited for achieving a multiuser diversity effect is selected, andthat in the frequency band f2 where the delay time suited for achievinga frequency diversity effect is selected. As in the case of FIG. 13, theinitial phase for the chunks K1, K2, K9 and K10 is p1, while the initialphase for the chunks K5, K6, K13 and K14 is p2.

In frequency band f1, a small delay is applied to achieve the multiuserdiversity effect, with the result that the transfer function has alarger delay-induced variation in the frequency domain than in thefrequency band f2. The peak values of the transfer function shiftdepending on whether the initial phase is p1 or p2. As a result, in thefrequency band f1, where the transfer function exhibits a relativelylarge variation, the average receive signal power differs greatlydepending on which is dominant, the higher peak value or the lower peakvalue. This results in the great variation in receive signal levelappearing every time the initial phase is switched as shown on the lefthand side of FIG. 14. It should be noted in this connection that, whenthe transmission path experiences only moderate change, the receivesignal level exhibits very little change for the chunks K1 and K9 wherethe same initial phase is chosen. The same applies to the chunks K5 andK13.

On the other hand, in the frequency band f2, a greater delay is appliedto achieve the frequency diversity effect, with the result that thedelay-induced variation in transfer function is smaller than in thefrequency band f1. Even in this case, the higher and lower peak valuepoints of the transfer function shift depending on the initial phasevalues set at the transmitter. However, average receive signal powershows very little change because of the very little change in the numberof the higher and lower peak values appearing in the frequency band.This is reflected in the right hand side of FIG. 14, where very littlechange is exhibited in receive signal power level even when the initialphase is switched.

It follows from the foregoing that an initial phase that provides ahigher receive signal level can be selectively set at the transmitter byswitching the initial phase particularly for those chunks where a largedelay is applied.

On the other hand, an initial phase that provides a higher receivesignal level varies depending on where the mobile unit is locatedbecause the locations involve mutually different transmission paths.FIGS. 15, 16 and 17 show examples of the reported transmission rate CQIfor three different types of terminal units (terminal units 12, 13 and14 shown in FIG. 9), which require the assignment of chunks suited forachieving a multiuser diversity effect. It will be noted that the higherthe receive signal level is, the higher transmission rate can bedemanded.

FIG. 15 shows in its upper part the frequency characteristics of thetransfer function for the terminal unit 12 with the initial phase set atp1 and p2. When the initial phase is p1, the bands f1 and f3 (i.e.,chunks K1, K3, K9 and K11) do not have any higher or lower peaks,resulting in a relatively large reported transmission rate values CQI asshown in the lower part of FIG. 15. When the initial phase is p2 on theother hand, the bands f1 and f3 (i.e., chunks K5, K7, K13 and K15) havelower peaks, resulting in a relatively small reported transmission ratevalues CQI.

FIG. 16 shows in its upper part the frequency characteristics of thetransfer function for the terminal unit 13 with the initial phase set atp1 and p2. When the initial phase is p1, lower peaks are present for thechunks K1, K3, K9 and K11, resulting in a small reported transmissionrate CQI shown in the lower part of FIG. 16. When the initial phase isp2 on the other hand, lower peaks are not present for the chunks K5, K7,K13 and K15, resulting in larger reported transmission rate CQI thanwhen the initial phase is p1.

FIG. 17 shows in its upper part the frequency characteristics of thetransfer function for the terminal unit 14 with the initial phase set atp1 and p2. With the general trend being similar to that of the terminalunit 12, the reported transmission rate CQI has a trend similar to thatof the terminal unit 12 as shown in the lower part of FIG. 17. Morespecifically, the reported transmission rate CQI for the chunks K1, K3,K9 and K11 is larger than that for chunks K5, K7, K13 and K15.

If the initial phase is fixed, the receive signal level at any one ofthe terminal units is kept low for a while, resulting in the request fora lower transmission rate, eventually lowering the throughput of thetransmission. For example, if the initial phase is fixed at p1, thereceive signal level at the terminal units 12 and 14 is maintained at afavorable value, while that level at the terminal unit 13 isdeteriorated. If the initial phase is fixed at p2 on the other hand, theterminal unit 13 only has a favorable receive signal level maintained,while the receive signal level at the terminal units 12 and 14 isdeteriorated.

The above problem can be resolved by selectively setting the initialphase values alternatingly. Description will now be given on schedulingto be performed at the base station for switching the initial phasevalues cyclically in the time domain.

Each of the mobile units sends to the base station the reportedtransmission rate CQI, which forms the reception quality information inthis embodiment. The base station performs the frame-by-frame schedulingon the basis of the information. A frame is intended to mean a unitconsisting of a plurality of consecutive slots extending to apredetermined length of time and occupying the entire frequency bandassigned thereto.

The base station averages the CPI values supplied from the terminalunits to determine the priority of each of the terminal units on thebasis of the averaged CPI values for each of the frequency bandsassociated with each of the initial phases. FIGS. 18A and 18B show howterminal units 12 to 14 are given the priority.

FIG. 18A shows the priority for the frequency bands f1 and f3 with theinitial phase set at p1. More specifically, since the CQI values fromthe terminal unit 12 in the chunks K1 and K9 are 10 and 10,respectively, as shown in FIG. 15, the averaged CQI value for theterminal unit 12 in the frequency band f1 with the initial phase p1 is10. Similarly, since the CQI values from the terminal unit 13 in thechunks K1 and K9 are 1 and 1, respectively, as shown in FIG. 16, theaveraged CQI value for the terminal unit 13 in the frequency band f1with the initial phase p1 is 1. On the other hand, since the CQI valuesfrom the terminal unit 14 in the chunks K1 and K9 are 7 and 6,respectively, as shown in FIG. 17, the averaged CQI value for theterminal unit 14 in the frequency band f1 with the initial phase p1 is6.5. Thus, in terms of the averaged CQI values for the terminal units inthe frequency band f1 with the initial phase p1, the priority is givenin the order of the terminal units 12, 14 and 13. In a similar manner,in the frequency band f3 with the initial phase p2, the priority isgiven in the order of the terminal units 14, 12 and 13. Similarly, asshown in FIG. 18B, the priority is given in the order of the terminalunits 13, 14 and 12 for the frequency band f1 with the initial phase p2,and the priority is given in the order of the terminal units 13, 12 and14 for the frequency band f3 with the initial phase p2.

An example of the scheduling is shown in FIG. 19, assuming thepriorities given as shown in FIGS. 18A and 18B. Further description willnow be given, assuming the frame-by-frame scheduling described above. Ina frame subjected to the scheduling, the chunk assignment is assumed tobe performed in the order of terminal units with lower to highertransmission rates.

In the first round, the assignment is performed starting with terminalunit 12. More specifically, to the terminal unit 1 is assigned the chunkK1, which is in the frequency band f1 with the initial phase p1 andgives the highest priority for the terminal unit 12. Then, to theterminal unit 13 is assigned the chunk K7, which is in frequency band f3with the initial phase p2 and gives the highest priority for theterminal unit 13. Then, to the terminal unit 14 is assigned the chunkK3, which is in the frequency band f3 with the initial phase p1 andgives the highest priority to the terminal unit 14. It is noted herethat the total of the averaged transmission rate values for the chunksassigned to the terminal units are 10, 6 and 9.5 for the terminal units12, 13 and 14, respectively. Subsequently to the first round assignment,the chunk assignment is performed in the order of terminal units withlower to higher total averaged transmission rate values. Morespecifically, to the terminal unit 13 is assigned the chunk K15, whichis in the frequency band f3 with the initial phase p2 and gives thehighest priority to the terminal unit 13. Since the total averagedtransmission rate for the terminal unit 13 is 12, the chunk K11 in thefrequency band f3 with the initial phase p1 giving the highest priorityto the terminal unit 14, which involves the lowest total averagedtransmission rate, is assigned to the terminal unit 14. Similarly, thechunk K9 is assigned to the terminal unit 12, while the chunks K5 andK13 are assigned to the terminal unit 13.

The scheduling performed in the manner described above reduces thetransmission rate differences among the terminal units, securingunbiased scheduling.

Another example of the scheduling is shown in FIG. 20, assuming thepriorities given as shown in FIGS. 18A and 18B. The chunk assignment tothe terminal units is performed for frames being scheduled, in the orderof the chunks K1, K3, K5, K7, K9, . . . and K15. When the dataassignment for transmission to a terminal of highest priority hasalready been completed, a terminal unit of the second highest prioritywill be assigned.

More specifically, to the chunk K1 in the frequency band f1 with theinitial phase p1, is assigned the terminal unit 12 according to thepriority shown in FIGS. 18A and 18B. Similarly, to the chunk K3 in thefrequency band f3 with the initial phase p1, is assigned the terminalunit 14 according to the priority shown in FIGS. 18A and 18B. Data fortransmission to the terminal unit 14 is assumed here to come to an end.Then, to the chunk K5 in the frequency f1 with the initial phase p2, isassigned the terminal unit 13 according to FIGS. 18A and 18B. Similarly,to the chunks K7 and K9, the terminal units 13 and 12, respectively.Although the terminal unit 14 is of highest priority in the chunk K11,the terminal unit 12 of the second highest priority is assigned to theterminal unit 12, because the data for transmission to the terminal unit14 has already been completed. To the chunk K13 is assigned the terminalunit 13 according to FIGS. 18A and 18B. Data for transmission to theterminal unit 13 is assumed to be completed at this point in time.Although the terminal unit 13 is of the highest priority in the chunkK15, the terminal unit 12 of the second highest priority is assigned,because the data for transmission to the terminal unit 13 has alreadybeen completed.

The scheduling performed in the above manner in the order of theterminal unit of higher priority to that of lower priority improves thesystem throughput.

In the present embodiment, the assignment of chunks to the terminalunits is performed in the manner described above based on the initialphase scheduling where the same initial phase value is chosen for everytwo consecutive slots.

While a method of scheduling has been described above by way of example,other methods may be employed as well. Even in those alternativemethods, the switching of the initial phase in the time domain to give agreater variation in transmission path characteristics, brings about theeffect of preventing the lasting deterioration of receive signal level.

In addition to the prevention of the continued deterioration in thereceive signal level by the switching of the initial phase values, thescheduling performed in the manner described above makes it possible toassign to each of the terminal unit's chunks of favorable conditions.More definitely, the switching of the initial phase results in steepervariation in the receive signal level, permitting the multiuserdiversity effect to be achieved.

Advantageous effects of the switching of the initial phase to achievethe multiuser diversity effect has been described above from theviewpoint that the multiuser diversity effect is achievable by causingsteeper variations in the receive signal level. In the frequencydiversity region, the advantages achievable from the switching of theinitial phase are limited. Therefore, the switching of the initial phasemay be applied only to achieve the region where the multiuser diversityeffect is to be achieved. However, the effect of the multiuser diversityeffect can be achieved, even when the switching of the initial phase isapplied independently of the distinction between the frequency diversityregion and the multiuser diversity region.

While the foregoing description of the embodiment is based on theassumption that the amount of delay is grouped in the frequency domain,with an initial phase having a fixed extension in frequency domain, themakeup of the embodiment is not limited to what has been described. Morespecifically, the amount of delay may be selected within a frame on achunk-by-chunk basis. Mutually different initial phase values may beselected at the same timing on a chunk-by-chunk basis.

The ratio of the number of chunks to which the initial phase values areapplied as shown in FIG. 21 may be adaptively controlled on the basis ofthe receive signal level reported from each of the terminal units. Inthe example of FIG. 21, since the reported transmission rate CQI forphase value p1 chosen as the initial phase is larger than that for phasevalue p2 chosen as the initial phase, the ratio of the phase value p1 isset at a large value.

By setting the ratio of the initial phase, for which a higher receivesignal level has been reported as described above, the system throughputcan be improved.

Second Embodiment

While the frame-by-frame scheduling has been performed in the firstembodiment described above, the slot-by-slot scheduling is performed inthe second embodiment.

FIG. 22 shows how the initial phase values are switched. The round triptime RTT, which is the amount of delay involved in the scheduling, is 4slots long. More definitely, assuming that a terminal unit produces thetransmission rate value CQI from a received slot for sending to a basestation including an rf signal transmitter of this embodiment and thatthe base station performs the scheduling on the basis of the CQI valuesupplied from that particular mobile unit, the slot assigned through thescheduling at the base station to that particular mobile unit is thefourth slot as counted from the slot which was referenced by that mobileunit for producing the CQI value for transmission to the base station.In FIG. 22, the repetition period Tco for the recursive switching of theinitial phase is two slots long. In other words, a first slot and asecond slot following the first one two-slot lengths later are of thesame initial phase. Thus, the repetition period Tco is one half of around trip time RTT.

As described above, the present embodiment is structured to have arepetition period Tco for the switching of the initial phase, which isequal to the round trip time RTT multiplied by the reciprocal of anatural number. Thus, the maximum number of the types of the initialphase is equal to the number of slots over which the RTT extends.

As shown in FIG. 22, the terminal unit 12 shown in FIG. 9, for example,measures the receive signal quality for the chunks K1 and K3, whichbelong to the group L11 with the initial phase set at p1 and the groupL13, respectively, and calculates the transmission rate CQI for thechunks K1 and K3, for transmission to the base station. Based on thesupplied CQI value, the base station performs the scheduling for thechunks K17 and K19, which belong to the group L11 with the initial phaseset at p1 and the group L11, respectively, and transmits the datathrough modulation/coding on the basis of the reported transmissionrate. Since the chunk K1 and K17 have the same initial phase and thesame amount of delay applied thereto and since the chunks K3 and K19have the same initial phase and the same amount of delay appliedthereto, the receive signal quality does not vary significantly, so longas the transmission path involves relatively small variation with time.As a result, the scheduling can be performed efficiently.

FIG. 23 shows an example of the relationship between the fluctuation ofthe receive signal level and the round trip time RTT for the scheduling.The relationship illustrated for the frequency band f1 is applicable toother frequency bands. The receive signal level for the terminal unit 12in the frequency band f1 is low when the phase p2 is applied comparedwith when phase p1 is applied. Since the large receive signal levelfluctuation is due to the switching of the initial phase, the repetitionperiod of a significant receive signal fluctuation depends on the periodat which the initial phase is switched. With the phase values p1 and p2selectively set at the two-slot long repetition period, the receivesignal level undergoes significant fluctuations at the two-slot longrepetition period. The transmission rate value CQI calculated from thereceive signal level for each of the chunks is used for the schedulingperformed in the chunk a four-slot long period later.

FIG. 24 shows an example of the receive signal level fluctuation at theterminal units 12 and 13.

Since the terminal unit 13 is located further from the base station thanthe terminal unit 12 is, the average receive signal level is lower forthe terminal unit 13 than for terminal unit 12. However, when theinitial phase is switched at the base station, the receive signal levelsviewed on a slot-by-slot basis may become higher for the terminal unit13 than the terminal unit 12. In the example shown in FIG. 24, thereceive signal level is lower for terminal unit 13 than for the terminalunit 12 when the initial phase is p1, while the receive signal level ishigher for the terminal unit 13 than for the terminal unit 12 when theinitial phase is p2. Since the receive signal level in the chunk K1 ishigher for the terminal unit 12 than for the terminal unit 13, thetransmission rate CQI reported in chunk K1 from the terminal units isgreater for the terminal unit 12. Therefore, the scheduling performed atthe base station based on the reported CQI results in a higher prioritygiven to the terminal unit 12 whose reported transmission rate ishigher. Thus, to the chunk K17 after the lapse of the round trip timeRTT is assigned the terminal unit 12. On the other hand, since the phasep1 is applied as the initial phase to the chunk K17 similarly to thechunk K1, the receive signal level is higher for the terminal unit 12than for the terminal unit 13. As a result, the required error ratio issatisfied to enable highly efficient data transmission. In a similarmanner, the terminal unit 13 is assigned to the chunk 21 for which thescheduling is performed on the basis of the chunk K5. This results inthe assignment of a terminal unit of a higher receive signal level tochunk K21.

As described above, the switching of the initial phase in thisembodiment at the repetition period of Tco results in a significantvariation in the transfer function. By setting the period Tco at alength equal to two slots, which is one half of the four-slot long roundtrip time RTT in this embodiment, and by assigning at the base stationto each of the terminal units the chunks based on the above setting ofthe repetition period, the assignment of the chunks to the terminalunits can be performed in an unbiased manner. Furthermore, since theassignment can be made to the chunks with the initial phase, whichprovides higher receive signal level, the multiuser diversity effect canbe achieved, enhancing the system throughput.

On the other hand, if the initial phase switching is performed withouttaking the round trip time RTT into account, the scheduling can beerroneously performed for a chunk with the phase p2 applied as theinitial phase, on the basis of the reported transmission rate CQI for achunk with the phase p1 applied as the initial phase. Under this state,since the initial phase associated with the chunk forming the basis forthe scheduling differs from that associated with the chunk beingscheduled, the transfer function of the associated transmission pathsmay come to fluctuate, resulting in a significant difference in thereceive signal quality. More specifically, if the chunk forming thebasis of the scheduling is in a favorable state in terms of the receivesignal quality while the chunk being scheduled is suffering deterioratedreceive signal quality, the error rate will increase due to theassignment of a terminal unit associated with a deterioratedtransmission path. In contrast, if the chunk forming the basis of thescheduling is suffering deterioration in receive signal quality whilethe chunk being scheduled in a favorable receive signal quality state,the scheduling cannot assign a terminal unit in a better receive signalstate, adversely affecting the spectral efficiency.

As described above, the setting of the repetition period Tco at a valueequal to the round trip time RTT multiplied by the reciprocal of anatural number makes it possible to perform optimal scheduling whileachieving the enhanced system throughput based on the initial phaseswitching or further unbiased scheduling for the terminal units.Compared with the first embodiment, the performance of the scheduling ata shorter repetition period provides the scheduling, which is responsiveto faster fluctuation in the transmission path characteristics.

While the scheduling in the above embodiment is performed by assigning aterminal unit of the higher reported transmission rate value CQI, theproportional fairness method may be employed in place of the aboveassigning method, thereby to assign the chunks to the terminal units ina more unbiased manner. This is because even a terminal unit, which islocated far away from the base station and which consequently has a verylow average receive signal level, can have a sufficiently highinstantaneous value of the transfer function relative to the averagevalue, due to the fact that the initial phase switching causes thetransfer function to fractuate significantly, thereby changing theinstantaneous value of the transfer function relative to its averagevalue.

It has been assumed in the above embodiment that the lengths of thedelay time are grouped in terms of frequency while the initial phase isfixed in terms of frequency. However, the delay time lengths maybeselected on a chunk-by-chunk basis within a frame as shown in FIG. 25.Even in the case where mutually different initial phases are selected ona chunk-by-chunk basis for the same timing, the similarly advantageouseffect can be achieved so long as the conditions are met where both thedelay time length and the initial phase become identical at therepetition rate of RTT for each of the chunks.

Third Embodiment

A third embodiment will now be described in conjunction with a specificmethod of the initial phase switching. FIG. 26 shows the phasedifference of two signals and complex amplitudes of the combined signal.If the phase difference between signals 1 and 2 is 0, the combinedsignal has a maximum amplitude in the state where the vectors indicativeof the complex amplitudes are in the same direction. As the phasedifference increases, the amplitude of the combined signal decreasesgradually to reach a minimum value for the phase difference of E. As thephase difference further increases beyond π, the amplitude of thecombined signal increases to reach a maximum value for the phasedifference of 2π.

As described above, the amplitude between the combined signal exhibitsthe variation with the change in phase difference between then twosignals from 0 to 2π. More specifically, when four different initialphase values are to be switchably set by two antennas, theantenna-to-antenna phase difference may be selected from 0, π/2, π, 3π/2and π to achieve the objective and thereby to bring about the adequatechange in the combined signal amplitude.

FIG. 27 shows an example of the switchable setting of theabove-mentioned four initial phases. Every time the phase difference ischanged by π/2, the positions of the upper and lower peaks of thetransfer function is shifted by a quarter of the upper-to-lower peakpitch and, when the phase difference is π, the positions of the upperpeaks and those of the lower peaks in the frequency characteristics arereversed relative to those for 0 phase difference. Furthermore, when thephase difference is 3π/2, the positions of the upper peaks and those ofthe lower peaks in the frequency characteristics are reversed to thosefor π/2 phase difference. To generalize, assuming the switchable settingof n different initial phases, the use of the n different initial phasesranging from 0 to 2π(1−1/n) at an interval of 2π/n makes it possible touniformly maximize the initial phase-based upper peak-to-lower peakshifts in the transfer function.

The initial phase switching performed in the order of 0, π/2, π, 3π/2 asshown in FIG. 27 need not be in that order. Similarly, the initial phaseassumed in the above description to be of constant value in thefrequency domain need not be that way, so long as the condition is metthat both the delay time length and the initial phase become identicalat an interval of RTT for every chunk. For example, instead of settingan initial phase of an antenna at a fixed value, the initial phaseapplied to two antennas, respectively, may be selectively set for bothantennas, in such a manner that the first antenna may receive the changein the order of 0, π/2, π, 3π/2, while the second antenna may receivethe change in the order of 0, π, 2π, 3π, thereby to provide the changein the order of 0, π/2, π, 3π/2.

The two transmit antennas employed in this embodiment may be replaced bymore than two such antennas, with at least one of them adapted to theswitched initial phase to achieve comparable results.

For example, if four transmit antennas are employed, one of them mayhave the initial phase switched in the manner described above.Alternatively, the initial phase may be switched only for the third andthe fourth antennas thereby to provide the phase difference 0, π/2, πand 3π/2 in that order, relative to the initial phase of the first andthe second antennas, with that for the first and the second antennasleft unswitched. It will be noted here that as the fluctuation of thereceive signal level at the terminal unit increases, the multiuserdiversity effect can be achieved.

It will also be noted that the method of selecting the initial phasedescribed for the present embodiment can be applied to the first and thesecond embodiments.

Fourth Embodiments

The operation of the first to the third embodiments described above willnow be further described in conjunction with the fourth embodiment,referring to additional drawings. The base station unit, i.e., thetransmitter unit of this embodiment is shown in FIG. 4. The base stationunit includes a packet data convergence protocol (PDCP) unit 15, a radiolink control (RLC) unit 16, a media access control unit 17 and aphysical layer 18. The PDCP unit 15 receives IP data packets, compressthem, transfers the compressed IP data packets to the RLC unit 16. Also,the PDCP unit 15 receives from the RLC unit 16 data and decompress theirheaders to restore them,

The RLC unit 16 transfers data received from the PDCP unit 15 to the MACunit 17. Also, the RLC unit 16 transfers data received from the MAC unit17 to the PDC unit 15. The MAC unit 17 performs the automatic repeatrequest (ARQ) processing, the scheduling-related processing, the datacombining/separation, and the control over the physical layer 18,thereby to transfer data received from the RLC unit 16 to the physicallayer 18 while transferring data received from the physical layer 18 tothe RLC 16. The physical layer 18 performs the conversion oftransmission data received from the MAC unit 17 into an rf transmitsignal, and the reception of an rf receive signal into the MAC unit 17,under control by the latter.

The MAC unit 17 includes a scheduler 19 for determining an assignedchunk for communication with the terminal units which are to be incommunication with the base station, and a transmit unit controller 20for controlling a transmit unit 21 using the subcarrier assignmentinformation based on chunk assignment information supplied from thescheduler 19, for controlling the antenna-to-antenna maximum delayresponsive to frequency diversity/multiuser diversity indicating signal,depending on the frequency diversity region or a multiuser diversityregion, and for controlling the initial phase at each of the antennas(or, more simply, the antenna-to-antenna initial phase difference)responsive to the initial phase information.

The physical layer 18 includes: the transmit unit 21 for performingmodulation under the control by the controller 20 in response to datareceived from the MAC unit 17, thereby to produce the data-modulatedtransmit subcarrier; an rf frequency conversion unit 23 forfrequency-converting the transmit subcarrier upward into higherfrequency rf signals and for frequency-converting receive rf signalsfrom antennas 24-26 downward into lower frequency rf signals forprocessing at a receive unit 22, which demodulates thefrequency-converted signal received from frequency conversion unit 23and provide the demodulation output to the MAC unit 17, and antennas24-26 for transmission and reception of transmit and receive signalsfrom/to the rf signal frequency conversion unit 23.

As described above, the transmitter of this embodiment includes thetransmit unit controller 20, the transmit unit 21 and the rf frequencyconversion unit 23.

For further details of the makeup of the structural elements of theembodiment described above, except for the scheduler 19, the transmitunit controller 20 and the transmit unit 21, reference is made to thepublication listed below:

“Evolution of Radio Interface Protocol Architecture,” June 2005,R2-51738, 3GPP (TSG RAN WG2 Ad Hoc).

The scheduling-related processing performed at the MAC unit 17 will nowbe described. As shown in FIG. 28, the MAC unit 17 includes thescheduler 19, which performs the scheduling-related processingincluding, as shown in FIG. 29, a step T2 for collecting thetransmission rate information MCS contained in the reported transmissionrate value CQI supplied from each of the terminal units, a step T3 forsequentially assigning the channels in the order of higher to lowertransmission rates for the terminal units, a step T4 for providing to atransmit unit controller 20 channel assignment information providedthrough the step T3 above, and a step T5 for deciding whether the nextframe (or slot) is to be transmitted and, depending on the decision, forreturning to the step T2 above or proceeding to the step T6, which is toend the processing. It is to be noted here that the transmission rateinformation, which constitutes the receive signal quality, is acquiredby the rf signal frequency conversion unit 23, the receive unit 22 andthe MAC unit 17 for supply to the scheduler 19.

While it is assumed in the description above that the transmission rateinformation MCS (Mobile and Coding Scheme) is supplied to the basestation, other information such as an average Signal to Interference andNoise Ratio (SINR) may be used in place of the MCS information, whichrepresents the quality of the rf signal received at each of the terminalunits from the base station.

Upon reception of the chunk assignment information through the step T5of the processing at the scheduler 19 above, the transmit unitcontroller 20 controls, in response to the chunk assignment information,performs control over the transmit unit 22 for the transmission of anext frame, using the subcarrier assignment information.

FIG. 30 shows examples of the transmission rate information MCSassociated with the process shown in FIG. 29. As shown in FIG. 30, theleft-hand column shows the MCS information in numbers 1-10, whichcorrespond to the type of modulation as applied and the coding rate forerror correction codes. More specifically, the information MCScorresponds to the transmission rates shown in the right hand column,indicating that the larger the number indicated in FIG. 30, the higheris the transmission rate required by the terminal units.

Referring to FIG. 31, there is shown a makeup of the transmit unit 21shown in FIG. 29. As shown in FIG. 31, the transmit unit 21 includessignal processors 110 x and 110 y for performing signal processing on auser-by-user basis, a pilot signal generating unit 120 for producingpilot signals for use at terminal units for estimation of transmitpaths, subcarrier assignment unit 130 for assigning the pilot signalssupplied from the pilot signal generating unit 120 to the subcarriers,and signal processing units 140 a, 140 b and 140 c for performing theantenna-by-antenna signal processing.

The user-by-user signal processor 110 x has an error-correction encoder111 for performing error-correction coding on transmission data, and amodulator for applying the QPSK, 16 QAM and the like modulation to theerror-correction coded data.

The outputs of signal processors 110 x and 110 y are assigned bysubcarrier assignment unit 130 to appropriate subcarriers in response tosubcarrier assignment information supplied from the transmit unitcontroller 20 (FIG. 28 referred to). The assigned subcarriers are thensupplied to antenna-by-antenna signal processors 140 a, 140 b and 140 c.It should be noted here that subscriber assignment unit 130 also has thefunction of assigning the pilot signal from generator 120 to the commonpilot channel (subcarrier) shown in FIG. 31.

The antenna-by-antenna signal processor 140 a receive the output of asubcarrier assignment unit 130 at a phase rotator unit 141 to apply themultiplication of a phase rotation of θm on a subcarrier-by-subcarrierbasis to supply the phase-rotated output to an inverse fast Fouriertransform (IFFT) unit 142. The signal processor 140 a further includes aserial-to-parallel conversion unit 143 for serial-parallel conversion ofthe output from IFFT unit 142, guard interval GI insertion unit 144 forinserting the guard interval to serial-parallel converter 143, filterunit 145 for selectively allowing only desired frequency band out of theoutput from GI adder unit to pass therethrough, and a D-A converter 146for D-A converting the output of filter 145. With antenna-by-antennasignal processors 140 b and 140 c having the same makeup as signalprocessor 140 a, the outputs from these signal processors 140 a, 140 band 140 c are frequency-converted at the rf signal frequency conversionunit 23 (FIG. 28) for rf transmission through antennas 24, 25 and 26(FIG. 28), respectively.

It is noted here that phase rotation additionally achieved at the phaserotation unit 141 is assumed to be θm=2πfm·(n−1)T+Φ, where fm stands forthe frequency spacing between the 0-th and m-th subcarriers, withfm=m/Ts, that Ts stands for the symbol length (length of time) for OFDMsymbols, that (n−1)T stands for the length of the circulating delay timeat the n-th antenna relative to the 1-st antenna. The circulating delaytime is used as a delay in the present invention, with Φ standing forthe initial phase. Since a specific subcarrier is used in a certainchunk, i.e., in either of the frequency diversity region or in themultiuser diversity region, transmit unit controller 20 (FIG. 28) forcontrolling transmit unit 21 indicates the use in either of thefrequency diversity region or multiuser diversity region throughfrequency diversity/, multiuser diversity indication signal, based onwhich the above-mentioned delay T is changed. It is noted that theinitial phase applied on a slot-by-slot basis or on a more than oneslot-by-more than one slot basis or on a chunk-by-chunk basis can alsobe controlled by the initial phase control signal supplied from transmitunit controller 20 for controlling transmit unit 21, based on which theinitial phase Φ is switched on a slot-by-slot basis, or on a more thanone slot-by-more than one slot basis or on a chunk-by-chunk basis.

While it is assumed in FIG. 31 that the number of the users and theantennas are two and three, respectively, these numbers are not limitedthereto.

If the rf signals are specifically scrambled signals involving scramblecodes applied on an antenna-by-antenna, sector-by-sector, or basestation-by basis station basis and, if such rf signals are transmittedan-antenna-by-antenna basis, the signal at a certain antenna may notlook to be only a delayed version of a signal from other antennas, suchdelay is also of the same category employed in the present embodiment.

Fifth Embodiment

This embodiment has a makeup similar to the fourth embodiment except forthe transmit unit 21. FIG. 32 shows in blocs the makeup of transmit unit21 employed in this embodiment. The transmit unit 21 includesuser-by-user signal processors 210 x and 210 y; a pilot signal generator220; and antenna-by-antenna signal processors 230 a, 230 b and 230 c forperforming signal processing associated with each of the signalprocessors.

User-by-user signal processor 210 x has error-correction encoder 211 forperforming error-correction coding of codes to be transmitted, modulator212 for applying QPSK, 16QAM and the like modulation to theerror-correction coded data, subcarrier assignment unit 213 forassigning the output of modulator 212 to an appropriate subcarrier onthe basis of the subcarrier assignment information supplied through anupper layer, an inverse fast Fourier transform (IFFT) unit 214 forperforming the frequency domain-to-time domain conversion of the outputfrom a subcarrier assignment unit 213, parallel-to-serial converter unit215 for performing the parallel-to-serial conversion on the IFFT output,and a circulating delay insertion unit 216 for insertingantenna-by-antenna delay time to the output from the parallel-to-serialconverter unit 215. The output from the circulating delay insertion unit216 is supplied to antenna-by-antenna signal processors 230 a, 230 b and230 c. It is to be noted here that the delay insertion unit 216 gives amutually different delay and initial phase on an antenna-by-antennabasis, in response to the frequency diversity/multiuser diversityindication information supplied from transmit unit controller 20 forcontrolling transmit unit 21. For detail reference is made to the firstto fourth embodiments described above.

The antenna-by-antenna signal processor 230 a includes a signalcombining unit 231 for combining signals supplied from user-by-usersignal processors 210 x and 210 y and for multiplexing the combinedsignal with the pilot symbols supplied from a pilot signal generator220, a guard interval (GI) insertion unit 232 for inserting GI to theoutput from combining unit 231, filter unit 233 for selectively allowingthe desired frequency band out of the output from the GI insertion unit232 to pass therethrough, and a D-A converter for D-A converting theoutput from the filter 233. With antenna-by-antenna signal processors230 b and 230 c having a makeup similar to the signal processor 230 adescribed above, the outputs from the signal processors 230 a, 230 b and230 c are frequency-converted at a frequency converter (not shown) intorf signal for transmission through antennas 24, 25 and 26.

While the description has been made above assuming the number of usersand antenna to be two and three, respectively, these numbers may begreater than those described.

When scrambling is applied on an antenna-by-antenna, sector-by-sector,or base station-by-base station basis by a specific scrambling code, asignal at one of the antennas may not look to be the simply delayed one,such mode of operation being included in this embodiment.

It is noted here that while the initial phase and the delay are given tothe phase rotating unit 141 in the fourth embodiment and to thecirculating delay insertion unit 216 in the fifth embodiment, theinitial phase may be given to the phase rotating unit, with delay givenat the circulating delay insertion unit. Similarly, the initial phasemay be given the circulation delay insertion unit, with delay given tothe phase circulation unit.

While preferred embodiments of the invention have been described andillustrated above, it should be understood that these are exemplary ofthe invention and are not to be considered as limiting. Additions,omissions, substitutions and other modifications can be made withoutdeparting from the spirit or scope of the invention. Accordingly, theinvention is to be considered as not being limited by the foregoingdescription, and is only limited by the scope of the appended claims.

INDUSTRIAL APPLICABILITY

The transmitter according to the present invention can be used in a basestation for a mobile communication system, such as, for mobile phones.

1. A transmission control method comprising: providing data to betransmitted through a plurality of antennas using regions defined byfrequency and time axes; providing the data to be transmitted with adelay that is constant along a portion of the frequency axis, whereinevery delay for each antenna is provided based on utilizing the cyclicdelay diversity; providing an initial phase to the data by applying afirst initial phase process, a second initial phase process, or thefirst initial phase process and the second initial phase process,wherein said first initial phase process includes: providing the data tobe transmitted with an initial phase that is variable along the portionof the frequency axis from one of a plurality of initial phases for eachof the regions such that the initial phase of each of the regions isdifferent from the initial phase of at least another of the regions, andsaid second initial phase process includes: providing a first initialphase to the data to be transmitted by at least one antenna of theplurality of antennas, and providing a second initial phase to the datato be transmitted by an antenna of the plurality of antennas, whereinthe first initial phase is a phase different from the second initialphase, and wherein said delay and said initial phase are providedtogether.
 2. The transmission control method according to claim 1,wherein said second initial phase is provided to the data to betransmitted by said antenna of the plurality of antennas such that saidantenna provided with said second initial phase is a different antennathan said at least one antenna that transmits the data provided with thefirst initial phase.
 3. The transmission control method according toclaim 1, wherein a first initial phase is provided to the data to betransmitted by at least two antennas of the plurality of antennas.
 4. Atransmitter comprising: a plurality of antennas; and a transmittingsection which is configured to: provide data to be transmitted through aplurality of antennas using regions defined by frequency and time axes;provide the data to be transmitted with a delay that is constant along aportion of the frequency axis, wherein every delay for each antenna isprovided based on utilizing the cyclic delay diversity; provide aninitial phase to the data by applying a first initial phase process, asecond initial phase process, or the first initial phase process and thesecond initial phase process, wherein said first initial phase processincludes: providing the data to be transmitted with an initial phasethat is variable along the portion of the frequency axis from one of aplurality of initial phases for each of the regions such that theinitial phase of each of the regions is different from the initial phaseof at least another of the regions, and said second initial phaseprocess includes: providing a first initial phase to the data to betransmitted by at least one antenna of the plurality of antennas, andproviding a second initial phase to the data to be transmitted by anantenna of the plurality of antennas, wherein the first initial phase isa phase different from the second initial phase, and wherein said delayand said initial phase are provided together.
 5. The transmitteraccording to claim 4, wherein said second initial phase is provided tothe data to be transmitted by said antenna of the plurality of antennassuch that said antenna provided with said second initial phase is adifferent antenna than said at least one antenna that transmits the dataprovided with the first initial phase.
 6. The transmitter according toclaim 4, wherein a first initial phase is provided to the data to betransmitted by at least two antennas of the plurality of antennas.
 7. Atransmitter comprising: a plurality of antennas; and a transmittingsection which is configured to: provide data to be transmitted through aplurality of antennas using regions defined by frequency and time axes;provide the data to be transmitted with a delay that is constant along aportion of the frequency axis, wherein every delay for each antenna isprovided based on utilizing the cyclic delay diversity; provide aninitial phase to the data by applying a first initial phase process, asecond initial phase process, or the first initial phase process and thesecond initial phase process, wherein said first initial phase processincludes: providing the data to be transmitted with an initial phasethat is variable along the portion of the frequency axis from one of aplurality of initial phases for each of the regions such that theinitial phase of each of the regions is different from the initial phaseof at least another of the regions, and said second initial phaseprocess includes: providing a first initial phase to the data to betransmitted by at least two antennas of the plurality of antennas, andproviding a second initial phase to the data to be transmitted by anantenna of the plurality of antennas, wherein the first initial phase isa phase different from the second initial phase, and wherein said delayand said initial phase are provided together.
 8. The transmitteraccording to claim 7, wherein said second initial phase is provided tothe data to be transmitted by said antenna of the plurality of antennassuch that said antenna provided with said second initial phase is adifferent antenna than said at least two antennas that transmit the dataprovided with the first initial phase.
 9. The transmitter according toclaim 7, wherein a first initial phase is provided to the data to betransmitted by at least two antennas of the plurality of antennas.